Capacitive sensors operate by detecting changes in the capacitance formed between a transmission electrode and a sense electrode. A sensing circuit can recognize an object and determine the location, pressure, direction, speed and acceleration of the object as it is approaches and/or moves across the touch surface.
Electronic devices with touch sensing surfaces may utilize various capacitive sensing devices to allow a user to make selections and move objects by moving their finger (or stylus) relative to a capacitive sensing element. Mutual capacitance touch sensors not only have the ability to detect touch events on the sensing surface, but also have the ability to detect proximity events, in which an object is not touching the sensing surface, but is in close proximity to the sensing surface. The mutual capacitive touch sensor operates by measuring the capacitance of the capacitive sense element, and looking for a change in capacitance indicating a touch or presence of a conductive object. When the conductive object (e.g., a finger, hand, foot, or other object) comes into contact or close proximity with a capacitive sense element, the capacitance changes and the conductive object is detected. An electrical circuit may be utilized to measure the change in capacitance of the capacitive touch sense element, and the electrical circuit may convert the measured capacitance of the capacitive sense element into a digital value.
The ability of the mutual capacitance touch sensors to detect objects in close proximity to the sensing surface is limited by the size and operating specifications of the electronic device. In an effort to reduce the size of electronic devices, the size of the operational components, such as microprocessor chips, printed circuit boards, displays, memory chips, hard drives, batteries, interconnectivity circuitry, indicators, input mechanisms, and the like, are also reduced. There is, however, a desire to maintain operational specifications, such as operating power specifications, while increasing the functionality of the touch sensor.
Capacitive sensors may also be utilized to measure a volume and/or a level of some material, such as fluids, within a container. Capacitive sensors utilized in such applications may provide a more accurate measurement and may be more reliable than conventional indicators.